This invention relates to the preparation of hydroxyarylaldehyes wherein a corresponding phenolic compound is reacted with formaldehyde, or a formaldehyde liberating compound in the presence of a catalyst such as a titanium or zirconium containing catalyst. Among other uses known to the art, the aldehydes are particularly useful as intermediates in the preparation of the corresponding oximes, which find utility as metal extractants.
The hydroxyarylaldehydes may be prepared by a number of routes. A summary and review of the synthesis of aromatic hydroxyaldehydes may be found in H. Fiege, K. Wedemehyer, K. A. Bauer, A. Krempel and R.G. Molleken, Frangrance Flavor Subst. Proc. Int. Haarmann Reimer Symp. 2nd, 1979 (Publ. 1980), pp. 63-73, which discusses in particular three processes of preparation.
One of these processes is the Reimer-Tiemann reaction which involves the reaction of a phenol with chloroform under very basis conditions to give the salicylaldehyde. Yields tend to be low and recovery of the product difficult. A recent patent, U.S. Pat. No. 4,324,922, relates to improvements in the process citing as further background Hans Wynberg, "Chemical Reviews", Vol. 60, 169 (1960) and Ferguson, "Chemical Reviews", Vol. 38, 229 (1946. Other U.S. Pat. Nos. 3,206,513 and 3,972,945 provide further background in relation thereto.
A second industrially useful approach involves condensation of the phenol with formaldehyde followed by oxidation with oxygen and a catalyst. While reasonable yields of salicylaldehyde are obtained, the process consists of two steps and involves the use of expensive catalysts. Illustrative of some of the patents relating to this process are U.S. Pat. Nos. 3,173,956, 3,321,526, 3,673,257, 3,780,110, 4,026,950 and 4,190,605.
Two other recent variations have been introduced. The first, which can be seen in U.S. Pat. No. 4,151,201, involves heating paraformaldehyde with phenol in the presence of anhydrous stannous chloride and pyridine. The second, which can be seen in U.S. Pat. No. 4,231,967, involves replacing the stannous chloride with an iron or chromium compound, preferably chromium acetylacetonate. Good yields are obtained via both processes. Both processes require relatively high levels of the catalyst promoter, pyridine, which must be recycled and requires special handling on an industrial scale. The presence of the heavy metals also presents problems in waste disposal. Further iron and chromium compounds tend to promote adverse side reactions.
Another process, which can be seen in U.S. Pat. No. 4,085,146 directed specifically towards production of alkylsalicylaldehydes, involves formation of a Mannich base, followed by oxidation and hydrolysis to the alkylsalicylaldehyde. While good yields are obtained, the process is economically burdensome due to the number of steps involved.
The invention herein finds particular utility in the process of preparing aldehydes using titanium or zirconium catalysts such as described in currently assigned, co-pending application U.S. Ser. No. 433,745 filed Oct. 12, 1982. Another similar process employing titanium catalysts in the preparation of alkylsalicylaldehyde in which the alkyl group contains from 1-10 carbon atoms is found in European Patent Publication 0077279 published Apr. 20, 1983.
It is an object of the instant invention to provide a method for improving the yield in the production of hydroxyarylaldehydes. Other objects will become apparent as this description proceeds.